Process for dry cationization of starch

ABSTRACT

A dry process for preparation of cationic starch ethers by reaction of starch with alkylidene epoxides in the presence of water in an alkaline medium at a temperature of 5° to 40° C. in the presence of a finely divided silica.

The invention relates to a dry process for preparation of cationicstarch ethers by reaction of starch with alkylidene epoxides in thepresence of water in an alkaline medium.

It is known from the prior art that starch or starch containingsubstances can be reacted in so called dry processes with cationicetherifying agents. In these processes the reaction is conducted not inan aqueous suspension but with pulverulent starch.

According to U.S. Pat. No. 4,127,563, alkylidene halohydrins at a pH of9 or lower and a temperature of 25° to 60 ° C. are used for thecationization.

The reaction of a halohydrin with starch in an alkaline medium, but at atemperature which lies at least 30 ° C. below the gelatinizationtemperature of the starch, is claimed in U.S. Pat. No. 3,346,563.

European Patent 31,477 also teaches a process for reaction of starchwith alkylidene epoxides, which is conducted in the presence of water,calcium hydroxide or calcium oxide at temperatures of 50 to 120 ° C.

West German Application No. 2,935,338 teaches a process forcationization of starch, in which, however, the alkali excess must beneutralized.

According to U.S. Pat. No. 4,281,109, it is recommended tht theetherifying reagent and the alkali metal or alkaline earth hydroxide bemixed together beforehand and only thereafter mixed with the starch.

By these procedures it is intended that more homogeneous and fasterintimate mixing of the reagents be achieved, so that, for example, highlocal alkali concentrations, which can lead to swelling of the starch,do not occur.

All cited processes have in common the feature that the reaction mixturemust be mixed until completion of the etherification reaction. Withdecreasing temperature the reaction naturally lasts longer. Reactionvessels are therefore utilized for just as long and cannot be used forother purposes, and stirring energy must be expended. In addition, yieldlosses have to be accepted and tolerated.

The object of the invention is to provide a process for preparation ofcationic starch ethers, in which, despite low reaction temperatures atthe same time only very little stirring energy is required, reactionvessels are only briefly tied up in the process and very good yields areobtained, in addition to which screening is not necessary.

The subject matter of the invention is a process for dry cationizationof starch by reaction of starch with alkylidene epoxides in an alkalinemedium in the presence of water, wherein the reaction is conducted at 5°to 40 ° C. in the presence of a finely divided silica. The pH of astarch prepared in this way is 9 or higher (5 weight percentsuspension).

The procedure according to the invention is that the mixture of starch,alkali metal or alkaline earch hydroxide or oxide, silica and alkylideneepoxide, which in general is used as an aqueous solution, is homogenizedin a intensive mixer for 10 seconds to 25 minutes, preferably 20 secondsto 5 minutes, then transferred out, and the dry cationization is allowedto proceed to completion in the designated storage receptacle such as,for example, a silo, or even in the packages provided for shipment.

Thereafter, further mixing energy no longer has to be expended forfurther process steps.

In addition, it proves advantageous to operate preferably in atemperature range within which, depending on, for example, seasonallyrelated fluctuations of the ambient temperature, the room temperature ofsimple warehouse stores, vary i.e., from 18° to 30 ° C., especially 20°to 25° C.

Tests show that the epoxide used is completely consumed by reaction. Ata temperature of 20 ° C. after 7 days, only traces of less than 10 ppmof epoxide per kg of starch are still to be observed.

Starches prepared by the process of the invention do not contain acoarse fraction and can be used without post treatment (screening).

Suitable as intensive mixers are, for example, plow mixers (continuousand batchwise), wetting flow mixers (continuous). Other suitable mixerscan be used.

To prepare cationic starch ethers by the process of the invention,native or modified starches or starch-containing substances of anydesired origin can be used. Native wheat, corn, tapioca or potatostarches are used with particular advantage.

According to the invention, the etherification of the starch isconducted with alkylidene epoxides of the general formula ##STR1## inwhich n is a number from 1 to 3 and R₁, R₂ and R₃ represent the same ordifferent alkyl groups with 1 to 4 carbon atoms or R₁ =benzyl, and X⁻represents chloride, bromide, sulfate or acetate, preferably chloride.One or more of such epoxides can be used in the process of theinvention.

The viscosity of starch pastes is greatly increased when the reactionwith the above mentioned epoxides is conducted in the presence of from0.5 5 weight percent of a compound which corresponds to one of thefollowing formulas: ##STR2##

These compounds are preferably used in a mixture with the epoxidesacccording to formulas (I) or (II) and can also exist therein in theform of the associated epichlorohydrins.

At the lastest in the reaction medium, the conversion then occurs to theepoxides according to formulas (III) to (V), which, react with thestarch.

Mixtures of this type are prepared advantageously by using, in thesynthesis of the epoxides with formulas (I) and (II), is is described,for example, in U.S. Pat. No. 3,135,782, the quantities of theappropriate tertiary amines necessary for formation of the proportionsspecified for the epoxides with formulas (III) to (V). However, theseepoxides or chlorohydrins can also be synthesized separately and mixedin the specified ratio with the epoxides according to formulas (I) or(II).

Per mole of starch, calculated as an anhydroglucose unit in the drysubstance, 0.005 to 0.500 mole of epoxide according to formula (I) or(II), preferably 0.01 to 0.25 mole of epoxide, is used in the process ofthe invention. From this results a degree of substitution (DS) of 0.005to 0.300, preferably 0.01 to 0.20.

According to the invention, the etherification of the starch with thealkylidene epoxides is performed in a medium which contains 10 to 35weight percent, especially 20 to 25 weight percent, of water and 0.2 to2.0 weight percent, especially 0.4 to 1.5 weight percent, of an alkalimetal or alkaline earth hydroxide or oxide, particularly calciumhydroxide or calcium oxide.

In addition to these components known from the prior art, 0.02 to 2.0weight percent, preferably 0.2 to 1.0 weight percent of a finely dividedsilica must be present in the reaction mixture, relative to the totalquantity thereof.

The finely divided, synthetically produced silicas in question can beprecipitated or produced by methods of flame hyrolysis, hydrophilic orhydrophobic. Such methods are well known and are described in the priorart.

The specific surface areas of silicas suitable for this invention rangebetween 60 and 700 m^(2/) g, preferably 100 and 450 m^(2/) g (BETmeasurement in accordance with DIN 66,131, N₂ absorption at thetemperature of the liquid nitrogen, preliminary thorough heating of thesample of 110 ° C.).

There is preferably used in accordance with the invention hydrophilicprecipitated silicas with a specific surface area of 190 to 450 m^(2/)g, especially a spray dried precipitated silica with a specific surfacearea of 190 m^(2/) g (BET measurement).

Mixtures of hydrophobic and hydrophilic silicas can also be used.

A pulverulent mixture of silica and the alkaline oxide or hydroxide,especially calcium hydroxide or calcium oxide (referred to as"activator" herein) is preferably used.

The activator contains 10 to 50 weight percent, preferably up to 40weight percent of silica. The difference relative to 100% is made up bycalcium oxide or calcium hydroxide.

However, it is to be taken into account that the activator must exist asa powder and in each case the quantity of activator which exhibits a pHof 9 or higher (5 weight percent starch suspension) in the end productis used.

The order in which the reagents are mixed is in general not to beregarded as critical. However, it has proved advantageous firstly to mixthe starch and activator, with each other, for example, in a batchmixer, for up to 10 minutes and thereafter to spray on the epoxide inthe form of an aqueous solution

The mixture obtained in the synthesis of the epoxide by reaction of thecorresponding halohydrin with alkaline substances, such as, for example,alkali metal hydroxide, can be used directly if the alkali metal halideformed thereby does not cause problems in the end product, such aspresent a danger of corrosion. This is neither washed nor neutralizedand can be used directly

Naturally, the neutralization which is customary in the art, as well asthorough washing out of the alkaline earth or alkali metal fraction inthe cationized starch can also be performed if these additional stepsappears to be useful in view of the intended application of the starch.

By means of the process of the invention it is also possible to preparehighly substituted cold water soluble starches with a degree ofsubstitution of 0.08 to 0.30.

If the operation is performed at existing room or ambient temperature, atemperature control system is not needed, either for the mixing deviceor for the subsequent reaction to completion; nevertheless the desiredproduct is obtained with high yields.

Additional reaction vessels are also superfluous, since after intensiveintimate mixing the reaction mixture can be poured, for example, intothe packages provided for shipment or into a storage silo and reacttherein. Thus, the method of the present invention does not require longresidence times in the reaction vessels.

The short residence time in the mixing apparatus simultaneously permitsfor the first time the dry cationization to be conducted continuously,whereas, because of the long mixing times, only batchwise cationizationof starch has been known and practical according to the state of theart.

By using various types of activator, the invention also makes itpossible for the first time to vary the viscosity of the correspondingstarch solutions and simultaneously to keep the degree of substitution(DS) of the starch constant.

The cationized starches that can be prepared according to the inventionare suitable for use, for example, as retention auxiliaries, asadditives to the pulp in paper manufacture for improving the paperstrength, in the size press during paper manufacture, as thickeners, asflocculents for sewage treatment and in the manufacture of gypsum.

The following examples are illustrative of the invention.

The following activator types are synthesized for the cationization ofstarches by intensive mixing:

    ______________________________________                                              Composition                                                             Type  (weight percent)        Bulk density                                    ______________________________________                                        PC-1  58% calcium hydroxide, ca. 97% content                                                                0.21                                                  42% silica                                                                    (spray-dried silica)                                                          (190 m.sup.2 /g)                                                        PC-2  66% calcium hydroxide, ca. 97% content                                                                0.22                                                  34% silica                                                              PC-3  52% calcium hydroxide, ca. 97% content                                                                0.18                                                  48% silica                                                              PC-4  75% calcium hydroxide, ca. 97% content                                                                0.25                                                  25% silica                                                              PC-5  82% calcium hydroxide, ca. 97% content                                                                0.27                                                  18% silica                                                              ______________________________________                                    

EXAMPLES

In examples 1 to 3, the reagent solution in each case contains 0.5weight percent of 3-chloro-2hydroxypropyl dimethylethanolammoniumchloride relative to 2,3-epoxypropyl trimethylammonium chloride. Theanalysis data relate to washed out samples (isopropanol/water, 80/20weight percent).

EXAMPLE 1

50 kg (0.2482 kmol) of native potato starch (water content 19.5%;insoluble nitrogen content 0.008%) is placed in a mixer. After additionof 6.44 kg of activator PC-2, mixing is performed for 5 minutes and5.137 kg of reagent solution, which contains 1.054 kg of 2,3-epoxypropyltrimethylammonium chloride, is metered in within 5 minutes via a nozzlewhile the mixer is running. Mixing is continued for a further 10 minutesand the contents are poured into a storage silo. After a residence timeof 24 hours at 20 ° C., a yield of 92.8% are analyzed. The degree ofsubstitution of the cationic starch ether obtained was 0.026. The starchcontent was 4%. The viscosity of a 3 weight percent starch paste was 450mPas (measured with the Brookfield viscosimeter at 20 ° C. and 100 rpm).

EXAMPLE 2

50 kg (0.2482 kmol) of native potato starch (water content 19.5%;insoluble nitrogen content 0.008%) is placed in a mixer. After additionof 1.006 kg of activator PC-5, mixing is performed for 5 minutes.Thereafter, 5.137 kg of reagent solution with a content of 1.054 kg of2,3-epoxypropyl trimethylammonium chloride, is metered in within 5minutes via a nozzle while the mixer is running, and mixing is continuedfor a further 10 minutes. Thereafter, the contents are poured into astorage silo.

After a residence time of 16 hours at 20 ° C., a yield of 92.2%, whichcorresponds to a degree of substitution of 0.0258, was analyzed. Theviscosity of a 3 weight percent starch paste was 56 mPas (measured withthe Brookfield viscosimeter at 20 ° C. and 100 rpm). The pH of 5 weightpercent starch suspension was 11.8.

EXAMPLE 3

50 kg (0.2482 kmol) of native potato starch (water content 19.5%;insoluble nitrogen content 0.008%) is placed in a mixer. After additionof 0.403 kg of activator PC-5, mixing is performed for 5 minutes.Thereafter, 5.137 kg of reagent solution with a content of 1.054 kg of2,3-epoxypropyl trimethylammonium chloride, is metered in within 5minutes via a nozzle while the mixer is running, and mixing is continuedfor a further 10 minutes. Thereafter, the contents are poured into astorage silo.

After a residence time of 3 days at 20 ° C., a yield of 91.4%, whichcorresponds to a degree of substitution of 0.0256, was analyzed. Theviscosity of a weight percent starch paste was 1800 mPas (measured withthe Brookfield viscosimeter at 20 ° C. and 100 rpm). The pH of 5 weightpercent starch suspension was 9.5.

EXAMPLE 4

50 kg (0.2707 kmol) of native corn starch (water content 12.2%;insoluble nitrogen content 0.035%) is placed in a mixer. After additionof 1.054 kg of activator PC-2, mixing is performed for 5 minutes and areaction mixture of 2.820 kg of 65% 3-chloro-2hydroxypropyltrimethylammonium chloride, 1300 kg of 30% sodium hydroxide and 2.893 kgof water is metered in within 5 minutes via a nozzle while the mixer isrunning. After a further mixing time of 10 minutes, the contents arepoured into a storage silo where, after a residence time of 24 hours at20 ° C., a degree of substitution of 0.0323, which corresponds to areaction yield of 89.8%, was determined by nitrogen analysis.

EXAMPLE 5

50 kg (0.2677 kmol) of native tapioca starch (water content 13.2%;insoluble nitrogen content 0.004%) is poured into a mixer. Afteraddition of 1.042 kg of activator PC-2, mixing is performed for 5minutes. Thereafter, a mixture of 2.483 kg of 73.6% 2,3-epoxypropyltrimethylammonium chloride (0.01205 kmol) and 5.384 kg of water ismetered in within 5 minutes, and mixing is continued for a further 10minutes and then the contents are poured into a storage silo.

After a residence time of 24 hours at 20 ° C., a yield of 88.8%, whichcorresponds to a degree of substitution of 0.0400, was determinedrelative to the 2,3-epoxypropyl trimethylammonium chloride used.

EXAMPLE 6

50 kg (0.2698 kmol) of a converted corn starch (size press starch) witha water content of 12.5% and an insoluble basic nitrogen content of0.040% is placed in a mixer. After addition of 1.050 kg of activatorPC-2, mixing is performed for 5 minutes at 20 ° C. Thereafter, 1.001 kgof 73.6% 2,3-epoxypropyl trimethylammonium chloride solution (0.00486kmol) and 5.817 kg of water are metered in within 5 minutes via a nozzlewhile the mixer is running, and mixing is continued for a further 10minutes. After a subsequent residence time of 24 hours at 20 ° C. in asilo, a reaction yield of 87.5%, which corresponds to a degree ofsubstitution of 0.0158, was analyzed.

EXAMPLE 7

200 kg (1.0805 kmol) of native wheat starch (water content 12.4%,insoluble nitrogen content 0.023%); 6678 kg of 2,3-epoxypropyltrimethylammonium chloride (73.6% active substance =0.0324 kmol); 20.854kg of water and 3.154 kg of activator PC-1 per hour are continuouslymetered into a continuous flow mixer and after an average residence timeof 10 to 60 seconds are conveyed into a storage silo.

The analysis after a residence time of 24 hours at 20 ° C. indicated anitrogen content of 0.226%, relative to absolutely dry starch, withoutinsoluble basic nitrogen, which corresponds to a DS of 0.268 and areaction yield of 89.3%.

EXAMPLE 8

100 kg (0.5208 kmol) of native potato starch (water content 15.55%,insoluble nitrogen content 0.010%) is placed in a mixer. After additionof 1.351 kg of activator PC-2 and 0.657 kg of 97% calcium hydroxide(0.0086 kmol), mixing is performed for 5 minutes and then 5.028 kg 21.5%3-chloro-2-hydroxypropyl trimethylammonium chloride (0.0172 kmol) ismetered in within 5 minutes while the mixer is running. After a furthermixing time of 10 minutes, the contents are poured into a storage silo.After a residence time of 7 days at 20 ° C., a reaction yield of 92.8%,which corresponds to a degree of substitution of 0.0309, was reached.

EXAMPLE 9

50 kg (0.2482 kmol) of native potato starch (water content 19.5%;insoluble nitrogen content 0.008%) is placed in a mixer. After additionof 0.644 kg of activator PC-2, mixing is performed for 5 minutes.Thereafter, 13.068 kg of 70.3% 2,3-epoxypropyl trimethylammoniumchloride (0.0606 kmol) is metered in within 5 minutes via a nozzle whilethe mixer is running, and mixing is continued for a further 10 minutesAfter a residence time of 24 hours at 20 ° C. (silo), a nitrogen contentof 1.382%, which corresponds to a degree of substitution of 0.187, wasanalyzed The yield was calculated as 76.6%.

The cationic starch obtained in this way is cold water soluble.

EXAMPLE 10

The starches prepared according to the invention do not contain anycoarse fraction and are therefore usable without post treatment(screening). The particle size distribution practically does not change.This means at the same time that the remaining cationization reactioncan proceed after homogenization, e.g., even in the shipping container.

Reagent: 2,3-epoxypropyltrimethylammonium chloride

1.0 weight percent Ca(OH)₂

0.5 weight percent silica

    ______________________________________                                        Potato starch                                                                              Particle size distribution                                       ______________________________________                                        Untreated, native                                                                          >100 μm 0.5%                                                                             <100 μm 99.5%                                   Cationized at                                                                          20° C.                                                                         >100 μm 0.6%                                                                             <100 μm 99.4%                               (DS 0.040)                                                                             40° C.                                                                         >100 μm 1.0%                                                                             <100 μm 99.0%                                        50° C.                                                                         >100 μm 2.9%                                                                             <100 μm 97.1%                                        80° C.                                                                         >100 μm 10.3%                                                                            <100 μm 89.7%                               ______________________________________                                    

EXAMPLE 11

According to the invention, it is possible to achieve a change in theviscosity of starch pastes at constant degree of substitution: Potatostarch (DS 0.026)

    ______________________________________                                                                Viscosity of 3% starch                                Product from test                                                                           Activator paste (20° C.)                                 ______________________________________                                        3             1.0% PC-3 1800      mPas                                        1             1.6% PC-2 1450      mPas                                        As 1, but with                                                                              2.1% PC-4 600       mPas                                        2             2.5% PC-5 56        mPas                                        ______________________________________                                    

EXAMPLE 12

Starches cationized by processes of the invention exhibit excellentretention values. These are measured by means of the DDJ test onsubstance suspensions consiting of

3 g/liter of pulp (50% beach sulfite pulp, 10% spruce sulfite pulp, 40%spruce sulfate pulp), 21 °SR and

2 g/liter of filler (China clay).

(D.W. Zunker, A. F. Breazeale, Tappi 66 (11) (1983) 37, K. W. Britt, J.E. Unbehend, Tappi 59 (2) (1976) 67, D. Abson, D. F. Brooks, Tappi 68(1) (1985) 76)

    ______________________________________                                        DDJ Test (Dynamic Drainage Jar)                                                                    Fines and filler                                                     Additive in %  in the                                                         (relative to   filler Retention                                   Starch type solid)         (g)    in %                                        ______________________________________                                        Without starch             0.149   0                                          Native potato starch                                                                      0.2            0.145   3                                                      0.5            0.149   0                                          Cationic potato                                                                           0.2            0.026  83                                          starch (DS 0.031)                                                                         0.5            0.008  95                                          (example 8)                                                                   Cationic potato                                                                           0.2            0.054  64                                          starch (DS 0.026)                                                                         0.5            0.022  85                                          (example 1) 1.0            0.004  97                                          ______________________________________                                    

This test exhibits a good correlation with the conditions of the papermachine.

EXAMPLE 13

By the addition of 0.5 weight percent of 3-chloro-2-hydroxypropyldimethylethanolammonium chloride to the 3-chloro-2-hydroxypropyltrimethylammonium chloride or 2,3-epoxypropyl trimethylammonium chloridecationization reagent, it is possible greatly to increase the viscosityof starch pastes, which as regards use in the paper industry leads tomuch better retention values and improved properties of the end product.

    ______________________________________                                        Potato starch DS 0.026                                                                             Viscosity (3% paste)                                     Reagent              80° C.                                                                           20° C.                                  ______________________________________                                        2,3-Epoxypropyl trimethylammonium                                                                  153 mPas   918 mPas                                      chloride                                                                      +0.5% 3-Chloro-2-hydroxypropyl                                                                     284 mPas  1450 mPas                                      ethanolammonium chloride                                                      ______________________________________                                    

The cationization is performed at 20 ° C. in the presence of 1.6 weightpercent of activator PC-2.

EXAMPLE 14 (Potato Starch, Theoretical DS 0.049) EXAMPLE 14

By addition of silica, a higher reaction yield is obtained duringcationization.

    ______________________________________                                                 Yield after 6 days                                                            at 20° C.                                                                           Flow behavior                                           ______________________________________                                        Without silica                                                                           91.4%          Inadequate                                                                    (does not run                                                                 out of 18 mm                                                                  opening)                                            0.50% silica                                                                             93.9%          Very good                                                                     (runs out of                                                                  2.5 mm opening)                                     ______________________________________                                         (Flow cups: inside diameter 90 mm, height 42 mm)                         

The silica is spray dried silica, 190 m² /g surface area.

Further variations and modifications of the foregoing invention will beapparent to those skilled in the art and are intended to be encompassedby the claims appended hereto.

The German priority application No. P 36 04 796.1 is relied on andincorporated hereby by reference.

We claim:
 1. A process for dry cationization of starch comprisingreacting starch or a starch containing substance with an alkylideneepoxide in an alkaline medium in water, at a temperature of about 5 to40 ° C. in the presence of a finely divided silica.
 2. The processaccording to claim 1, wherein a mixture of starch, alkaline hydroxide oroxide, silica and alkylidene epoxide are mixed together to form areaction mass.
 3. The process according to claim 2, wherein the reactionmass is homogenized under intensive mixing for 10 seconds to 25 minutesin a reaction zone.
 4. The process according to claim 3, furthercomprising transferring the reaction mass out of the reaction zone andpermitting the mass to react to completion in a storage receptacle.
 5. Aprocess according to claim 1, wherein the starch is a native or modifiedstarch.
 6. The process according to claim 1, wherein the finely dividedsilica is a synthetically produced silica.
 7. The process according toclaim 1, further comprising homogenizing a mixture of starch, a alkalinecompound, silica and alkylidene epoxide under intensive mixing for 10seconds to 25 minutes, in a reaction zone to form a reaction mass,removing said mass from said zone to a storage zone to permit thereaction mass to react to completion.
 8. The process according to claim1, wherein a alkylidene epoxide of the formula ##STR3## in which n=1, 2or 3, R₁, R₂ and R₃ represent the same or different alkyl groups with 1to 4 carbon atoms or R₁ represents the benzyl group, and X⁻ representschloride, bromide, sulfate or acetal, or a mixture thereof is used. 9.The process according to claim 7, wherein an alkylidene epoxide of theformula ##STR4## in which n=1, 2 or 3, R₁, R₂ and R₃ represent the sameor different alkyl groups with 1 to 4 carbon atoms or R₁ represents thebenzyl group, and X⁻ represents chloride, bromide, sulfate or acetal, ora mixture thereof is used.
 10. The process according to claim 8, whereinthe cationization is realized in the presence of 0.5 to 5 weightpercent, relative to the epoxides with formulas I or II, of a compoundwhich corresponds to the following formulas: ##STR5## with X⁻ :chloride, bromide, sulfate or acetate (Ac).
 11. The process according toclaim 9, wherein the cationization is realized in the presence of 0.5 to5 weight percent, relative to the epoxides with formulas I or II, of acompound which corresponds to the following formulas: ##STR6## with X⁻ :chloride, bromide, sulfate or acetate (OAC).
 12. The process accordingto claim 1, wherein a pulverulent mixture consisting of silica, analkaline hydroxide or oxide is used.
 13. The process according to claim1, wherein a finely divided hydrophillic silica is used.
 14. The processaccording to claim 1, wherein a finely divided hydrophobic silica isused.
 15. The process according to claim 12, wherein water is alsopresent.
 16. The process according to claim 1, wherein the starch isselected from the group consisting of native wheat, corn, tapioca andpotato starch.
 17. The process according to claim 1, wherein thereaction is carried out for 20 seconds to 5 minutes.
 18. The processaccording to claim 1, wherein the alkaline compound is an alkali metalor alkaline earth metal hydroxide or oxide.
 19. The process according toclaim 1, wherein the alkaline hydroxide or oxide is calcium hydroxide orcalcium oxide.
 20. The process according to claim 1, wherein 10 to 35weight percent water and 0.2 to 2.0 weight percent alkaline compound ispresent.
 21. The process according to claim 1, wherein the silica ispresent in the amount of 0.02 to 2 weight percent.
 22. The processaccording to claim 1, wherein the finely divided silica has a surfacearea of 60 to 700 m^(2/) g.
 23. The process according to claim 1 whereina plow mixer is used to provide the intensive mixing.
 24. The processaccording to claim 1, wherein a wetting flow mixer is used to providethe intensive mixing.